The Liar Paradox - an explanation of the paradox from 400 BCE

[@talonthehand]

In the book Thief of Time by Terry Pratchett, the auditors of the universe, beings of pure order and logic, eventually overcame this paradox by classifying three types of sentences: True, False, or Bloody Nonsense.

[@stevehorne5536]

Para = beyond/aside from - let's say separated from. Dox = opinion/idea/belief - let's say sense. So a paradox is separated from sense - i.e. in the modern vernacular of Ankh-Morpork, bloody nonsense.

[@stevep2448]

And this demonstrates clearly the genius of Pratchett.

[@stephengibbs8342]

he was a genius

[@damiaomedeiros8873]

Thief of Time, one of the most delicious books ever writen!

[@mrtonod]

Reminds me of the caption in my Statistics 101 textbook which proudly stated that there are , "Three kinds of lies, lies, damned lies and statistics."

[@davidantonson9003]

This paradox is instantly relatable to anyone who takes an exam from a professor who isn't careful with their grammar and sentence structure. I am often stuck between wondering if the question is a "trick" or just not thoroughly thought out.

[@domomitsune5920]

This kind of reminds me of how my teachers used to teach the lessons, and told us to write everything down because it was going to be on the exam. But when you took the exam, they worded the questions so unintentionally, that you had a does not compute situation, and your brain started to fry itself trying to figure out what the hell the answer supposed to be, even though you knew the answer. Because the teacher said this was going to be on the test.

[@ENFPerspectives]

Ha. Exactly.

[@carlhartwell7978]

Definitely relate, grammar can be a bitch, but so can philosophy. Combine them and even the most experienced and knowledgeable tutor can be 'strung up'!

[@VKEvilution]

"Choose the answer that's least wrong"

[@robertcowan7610]

Been there. It sucks.

[@donwanna3906]

I feel like making it into two sentences instead of one doesn’t eliminate self-reference, just elongates it from one sentence to two. The set of two sentences is self-referential in the same way the set of one sentence was self-referential.

[@lozzamoore]

Really enjoying these videos. Yes so to my mind (with no formal philosophy training) the paradox arises due to the existence of a circular reference. Remove these from any set of sentences. Problem solved! I'm sure I'm missing something here....

[@jeffwells641]

It's more recursive than self reference. You could say a recursive system can't make reliable statements about itself.

[@TheSwiftCreek2]

I was also kind of thinking of dual self-reference, but I wasn't convinced I was right.

[@TheSwiftCreek2]

@@jeffwells641 Good point.

[@Fuckyoubloodymoron]

Circular logic be circular.

[@jeffreytackett3922]

I've always felt that this kind of thing isn't a limitation of math or human understanding, it's a limitation of language. In an odd but simple example, there are an infinite number of decimal steps between the number 0 and 1, but there are no (or very few) widely-accepted steps between false and true.

[@DemiImp]

It isn't a limitation of language. It is an intentional choice that "true" means "completely true". An equivalent is true means 1 and false means 0. If the value is 0.5, then it is either true (1), not true (not 1), false (0), or not false (not 0). In the 0.5 example, it is both "not 0" and "not 1", so it it satisfies both "not true" and "not false". Typically when people say something is false, they mean "not true". Or rather that the statement is not completely true. An example of this is "Hobbits are small humans". It is true that Hobbits are small, but it is false that they are humans. People will say that the statement is "false" as a shorthand for "not completely true".

[@wingstrongwingstrong]

a sentence as such is not binary maths and can be not only "true" or "false", it can also be "an incorrect set of words", so there is a third option: "the sentence is rubbish"

[@hicri9739]

That's one of the (not so great) options but you can formally express the paradox too. Language is what conveys you the paradox but not the paradox itself

[@peterskove3476]

I very much a novice in this area but I was wondering about that very thing as I listened. Then I wondered if this problem arises in the real world , or just a puzzle…and if that’s a measure of it being a language thing…

[@laszlobandi6456]

@@peterskove3476 arguing with a woke idiot and they claiming to be offended, if you say sorry or explain that they are overly emotional it's a lose lose scenario. XD there was a practical psychological theory regarding to dating which is kinda similar, I tested it and it's kind of fun. play a game where you tell a statement about yourself, which can be a truth or a lie. they got to decide which. at the end they got to explain why they thought it or you explain why is true/false. if they guessed it right they go again or up to 3x or forever. if they guess it wrong you swap. in a normal conversation you could be value signaling or ignoring stuff or secretly thinking it's a lie. helps clear prejudictions and judgemental thinking quite quickly. not the same theory but like similar. I think paradoxes can be funny, some jokes are like that. philosophers like to explain it for some reason.

[@drzonbrone3346]

Yes, the splitting into 2 sentences might remove self-reference, but it introduces it's own referential problem. You can replace the "The sentence below" with the actual sentence below. Similarly with the sentence above. You get into a similar infinite regression.

[@anxez]

That's where I was at. Which means you can ban all logic based on any loop of truth, and we already do that by calling out circular logic.

[@vincentc9072]

It's like an indirect self-reference

[@lorefox201]

in short, the two sentences don't exist in a vacuum by definition they are linked by referencing one another,so saying that you can do liar paradoxes by making liar PERIODS instead of liar SENTENCES is just... more recursion.

[@nilespierson]

That's exactly right. Splitting into two sentences doesn't remove the self-reference, it's just a higher order of self-reference.

[@benheideveld4617]

Indeed! The problem lies with referencing. According to Aristotle in his essay “On Interpretation” the requirement of a proposition is that it needs both a subject and a predicate. Kaplan erroneously uses the word sentence, but a sentence does not need to be true or false, a proposition in ordinary logic must be either true or false, but that doesn’t mean you can know if it is true or false. There are other tricks too, like “The final digit of π in decimal representation in unknown.” In order for this sentence to be a proposition, “The final digit of π in decimal representation” pretends to be the subject. But we all know that π has no final digit, because it’s decimal expansion is unending. Therefore the phrase purporting to describe the subject is describing an impossibility, therefore the purported subject is invalid as a subject. Therefore the sentence lacks a subject. Therefore according to Aristotle the sentence isn’t a proposition. Therefore the sentence cannot have a truth value. A subject containing a reference that does not completely materialize, here meaning lose all reference elements after a finite number of substitutions, just isn’t a valid subject and without subject we don’t have a proposition and a sentence that isn’t a proposition cannot have a truth value and hence cannot yield a paradox.

[@ericpheymannicie5044]

The 1986 film *Labyrinth* has a very well-hidden reference to this paradox in the 2 Doormen Riddle scene. Sarah is tasked with the riddle "You can only ask one of us [which door leads to the castle]," "[but] one of us always tells the truth and one of us always lies." Sarah thinks she figures this out by asking one doorman "would [the other doorman] tell me that this door leads to the castle?" She receives the reply "yes" and concludes that the other door must lead to the castle based on a similar self-reference liar quasi-paradox. Sadly she fails the riddle, and to the audience, it seems to be written off as just one more example of how the Labyrinth is "not fair." Except there's a beauty to *why* she failed. Her logic seems sound and very well could be, except for the fact that the rules were recited to her by the very doormen who claim to be a lying/truthful pair. So trying to break down the logic of whether the rules themselves could be true or not true reveals the true paradox: Can the person who says "one of us always lies" be telling the lie? A simpler breakdown is based on the fact that the two rules, "One of us always tells the truth/always lies," and "you can only ask one of us," are each recited by a different doorman. Assuming that the one who recites the truth/lie rule is lying breaks the riddle entirely and leaves no assurance that either doorman is bound or even willing to tell the truth; while assuming that the one who recites the truth/lie rule is telling the truth breaks the solving process entirely, and concludes that the 'you can only ask one of us' rule must be a lie so you have plenty of opportunities to interrogate both doormen. In fact, in assuming that the truth/lie rule is truthful, you lock yourself into assuming that the doorman who recited that rule is the only one you should ask anything. Underlying truth be damned, if you believe that rule, you *MUST* logically believe that you have already solved the riddle (though if the riddle is real, you may not have and can never really know). Sure, it really is just another example of how the Labyrinth is "not fair"; but isn't it so much more sinister knowing why? Also, everything I just said is a lie! =P

[@ridestreet20]

Fuck.

[@georgemaragos2378]

Hi, this was done earlier in Dr Who with Tom Baker - Pyramids of Mars It was well explained If he asked the "truth" guardian where would the other guardian point to as correct exit the truth guardian would point to the false door - death If he asked the "lying/false" guardian which door would the other one point to he would lie and also point to the death door The analysis was that both answers would highlight the lie every time so the other exit was the correct one

[@Frankie726]

​@@georgemaragos2378 i think the original comment takes it one step further by stating: if these rules are told by the brothers, (of which one is lying) that must mean that the rules are a lie. Which creates a new set of problems like: maybe they are both always lying. But you will never know for sure, and that makes it unsolvable

[@cyrosgold7]

I like how they handled this riddle in episode 5 of Journey Quest. Where the guy presented with the riddle kills one of the door keepers(the one that speaks truth) the asks the other which way is correct. Then tells him that if he is lying he would kill him and asks if he understands. The door keepers says no, so the guy asks if he wants to die so the door keepers says yes, and the guy throws him through the door that is thought to lead to doom and when the door keepers doesn't die the guy seduces that that is the safe pass. The lying doorkeeper eventually becomes the guy's squire by always flattering him and being his "yes" man.

[@sansivian]

I’ve never understood this paradox as how that particular sentence is “false” or “true” as there is no object.

[@Paulsinke]

Why can't we just let the word "paradox" be the solution to this? It is true or false? No, it's a paradox. Thanks for all your work making these videos, I'm really enjoying them

[@Exception1]

Probably because they always try to force the sentence into a classical logic-ish interpretation. Like he did with the "this sentence is not true" example. Then used axioms and inference rules of classical logic on it to generate a contradiction. But in classical logic... a sentence that is true and false or neither is not a sentence at all. (well not a "proposition").

[@njsmeets66]

I concur. Our universe should contain, must contain, needs to contain mysteries.

[@thaddeuspawlicki4707]

Because you would have to consider the statement ; "This sentence is not a paradox"? In essence "paradox" == "Neither True nor False". Introducing a new term doesn't solve the problem.

[@stepheneickhoff4953]

Like the definition of x/0?

[@keystothebox]

False, paradoxes do not exist

[@marcdraco2189]

That self-reference to your bald spot knocked me off my stool Dr. Kaplan. Salute sir!

[@iluxa-4000]

With situations like this, I always propose the thought of "it has no meaning". In this case - some sentences are true, some are false, and some have no meaning behind them, thus not worthy of a thought. The pair of sentences that reference each other and create a paradox don't posses any meaning, so they should be treated as just that - a jumble of words

[@philcorrigan5641]

Yes, similar to how the correct answer to dividing by zero is that it is ‘undefined’. Or to put it another way: garbage in, garbage out.

[@Charles.Martin]

@@philcorrigan5641 I just had this same thought when watching the video!

[@Squant]

That's just a less eloquent, and potentially incorrect way of saying "neither true nor false".

[@iluxa-4000]

@@Squant em, no. You just refuse to play the game because it makes no sense, that's all

[@dragonslair951167]

@@Squant Take a sentence that doesn't contain a claim, like a command: "Go fetch me some milk." Or a question: "Who are you?". You could technically say that the sentence is "neither true nor false" and therefore "not true", but in doing so you're stretching the definition of "untrue" to the point where it simply makes no sense to use it linguistically. "That command is untrue" or "That question is untrue" is wordplay at best and gibberish at worst. The logic you're using operates under the false dichotomy that something can either be true or untrue and there's nothing in between or outside that. But sometimes something IS in between, half true, or (Most importantly) simply irrelevant or meaningless.

[@BellCube]

I propose that we introduce alongside "true" and "false" a new term by the name of "repeatitively recursive." As a computer scientist, I'm most use to such a concept. If a program with inputs X calls somewhere in its executions itself with inputs X, it will therefore repeat until halted hy some external factor (such as the power being yanked). Remember, things like time and user clicks can be considered inputs. In such a case, you will never get an output of any kind; all you'll see is a loading spinner. I feel that formal logic should have a term for this.

[@AllanHytowitz]

The essential duality of the Universe is how Edwin Schrodinger came up with his classic theory where he named his two cats Anny and Sheila after his wife and mistress.

[@ellenmarch3095]

We do, it's called "endless loop".

[@nilsbabcock7686]

We should call it Schrodinger's Sentence.

[@ccoder4953]

In logic circuits, we often allow such things, in fact we even design them. The most basic example is the ring oscillator - just an odd number of inverters (n>1) connected in a loop. Many oscillator designs have some form of that at their core - self contradictory logic. They might have a bunch of analog trickery to get better timing, but at their heart, they are just some form of logic that can't make up it's mind which state it should be in.

[@SeanJMay]

​@@ccoder4953 always saw that more akin to a pendulum. The potential is transferred and thus gone, but it comes back around again. Not necessarily paradoxical because you can trace it through time, even if we’re talking about speeds akin to the speed of sound through nanometers of copper. It becomes a ridiculously fast NASCAR race, full of nothing but left-hand turns. In the same way, languages that aren't based on stack frames are generally more amenable to running recursively in perpetuity, whether singularly recursive, or mutually recursive. Most Lisp languages (that aren't built on top of Java) for instance could happily oscillate back and forth to the heat death of the universe (or random traces on the motherboard, whichever comes first).

[@Adyen11234]

I think the most amazing thing about humans is the ability to stop thinking about things like paradoxes.

[@ChipsMcClive]

That’s because language was made to save energy instead of spending more of it.

[@contrawise]

Seems I don't have that ability. Like it.or not, I keep seeing them.

[@jeremyashford2115]

I see dead theories.

[@NashvillePastaman]

I see “Mostly” dead theories!!!

[@DePhoegonIsle]

Eh, because alot of people instantly see this as invalid. Regardless true or false, it is invalid as it violates the given ruleset it proposes. More paradoxes than you might think end up being invalid because humans are just masters at breaking things. With some being closer to untested Exploitive things and lack the deeper knowledge to either resolve the truth of it or make it clear it isn't possible outside imagination & fiction. Paradoxes often happen because of a VERY simplistic take on a system with much deeper understandings required, and past that are invalidated because it was crafted to be that way. Just like we view those who think flying is proof of either a paradox or conspiracy as idiots... in time we will view those who honestly believe such paradoxes in earnest as fools as well. The issue is 'we do not fully understand what we need to' for alot of these paradoxes, and some are just people being douches and breaking a system because they can.

[@NeedsContent]

I'm just impressed he's able to write everything backwards so well.

[@GlutenEruption]

Can’t tell if this is a joke or not but in case anyone doesn’t know, you just write normally and then mirror the video in the edit.

[@NeedsContent]

@@GlutenEruption Well that would make a lot more sense!

[@BOOGY110011]

You my friend should watch some "shapes and colors" type of video. Might to early for paradoxes for you hehe

[@rebelsclipsntricks]

When he wrote the sentence "fribble is not true." But wrote the sentence in backwards order from true to fribble, to much lol

[@User24x]

@@GlutenEruption I didn't know either

[@janschwart4060]

I've watched a lot of his videos now and I must say I'm just absolutely flabbergasted by how well he's able to write backwards on that glass pane

[@tomboyd7109]

He is writing normally and the camera is inverting it. Look at his wedding ring. Some new U-Tubers have not figured out how to fix that camera glitch. He is simply using it.

[@omnipop4936]

@@tomboyd7109 Yup, the ring, and his watch, and his shirt buttons...

[@goldmirado3]

Ahh new here?

[@what6306]

lol they just flip the video so its readable lady

[@mutasimaldory]

Interesting..I simply assumed he was writing on a mirror, not a glass window, and the black background was to mask the camera; I never imagined anyone would see it any other way! 😂

[@llywyllngryffyn8053]

The Two sentence paradox or really any multiple sentence version of the paradox suffers from the same Self-Reference issue. It is an issue of recursion. You have to ban all recursive references and a final evaluation of truth must be reserved for a sentence whose references have been replaced with their target representations. The reference "The Sentence Blow" is true must be replaced with the actual sentence blow. So when you do this, that sentence contains another reference which must be resolved before a final sentence can be established. in your example, that would make the reference Null since it points to something that no longer exists. You cannot form this paradox without depedent references.

[@korbyd236]

I hate how he said the sentence "this sentence is not true" can't be neither true not false because it can like this sentence isn't true ok then it's false no then it's true no ok so it's neither true not false

[@korbyd236]

And then bro pulled the if it's Accurate it's true and I was like that's an ass pull it pissed me off cuz like yes technically you could do that but when the "this sentence is false" it doesn't apply then it wouldn't with not true as well or it would apply to both the same way

[@kalanivernon7273]

The fundamental problem isn’t recursion. Recursion is a symptom. The fundamental problem is the inability to resolve any kind of mutual exclusivity when both options are EQUAL. And this goes back to a fundamental and flawed assumption in logic itself: That there is always a better/more accurate/superior option. And baked into that assumption is a second assumption: That logic itself is always the superior option to resolve X. Without even realizing it, every one of us who relies on logic has a secret belief we may not be aware of: Logic is always the superior option to resolve X. If X cannot be resolved by [current understanding of logic], [current understanding of logic] is flawed. Ergo: A perfect, pure form of logic must exist that can resolve all variables of X. At no point is the first premise ever countered. Deep down in our souls, we believe there is a pure, omega logic that perfectly resolves everything. Every possible paradox; Every possible scenario; takes into account every possible variable; and with perfect results every time. This is an unfalsifiable assumption, and for reasons that baffle me - completely rejects the Null Hypothesis without even attempting to prove the premise is true. My premise: Logic may not always be the superior option to resolve ALL instances of X, and by extension - no perfect, pure, omega logic exists. For example - to the best of my understanding, logic cannot be used to solve the following: A has a value of 2 B has a value of 2 Choose the option with greater numerical value. A or B. (And the question provides a radio button with which to select your response). Since you cannot enter both/neither, or an another answer of your choosing (and are limited to choosing A or B as your only answers), this question cannot be resolved without relying on something other than logic (personal bias, random selection, etc).

[@dougaltolan3017]

​@@kalanivernon7273 The problem is not (and cannot be) logic, since logic is rigourosly defined to be correct. The problem is the presumption that language must be logically correct. This and other so called paradoxes merely show that language lacks rigid (logically correct) semantic rules.

[@dougaltolan3017]

​@@kalanivernon7273 Ohh, and to answer your question: B in virtually all cases... While A and B might have the same value, B has a greater name. In fact, B is the correct answer regardless of the values of A and B since your question only asks for the greater option, not the greater value of the option.

[@ingvaraberge7037]

The liar paradox reminds me of the rule in mathematics that says that one can not divide by 0. One can write for example 5/0, but it gives no mathematical meaning. Any answer you come up with will be wrong. In a similar way, if a sentence has as a consequence the denial of the sentence itself, that sentence is logically impossible.

[@irgendwieanders2121]

Chuck Norris can divide by 0!

[@nicomoreno5028]

​@@irgendwieanders2121 lol Chuck Norris's beard can divide by zero.

[@irgendwieanders2121]

@@randomrandomizer You can also define 0/0=1 Depends on your choice of axioms...

[@ingvaraberge7037]

@@randomrandomizer That doesn't sound too wrong. Until you try it the other way around and multiply infinity with zero. How long you continue the row 0+0+0+0+...., you'll never make it to 5. Or to put it the other order: Zero infinities is not 5. So your answer doesn't work, even though your suggestion is a tempting conclusion.

[@gm2407]

If Zero Mostel had a high school diploma than he understood basic maths. At one point he must have proved he understood division. Therefore at one point something was successfully divided by 'Zero'.

[@glenmassey3746]

That was one of the best episodes in sci-fi that shows how to defeat an advanced AI. If that AI, has to answer the question that uses a paradox before doing another question or action and it might stop the AI or slow it down till it can answer that question.

[@starroger]

Computer, compute to the last digit the square root of 2.

[@zeekfromthecreek]

Unfortunately, I don't think the AIs we're about to replace ourselves with will fall for it.

[@ratherbefishing-r4u]

You're thinking of Artificial Stupidity. Artificial Intelligence already exists. Try presenting this "paradox" to ChatGPT. First of all, no A.I. would ever be programed in such a way as to preclude it from moving on if it couldn't find an answer. Second, a true A.I. reacts in a similar way to what a human would. That's the entire idea behind them. So any sufficiently advanced A.I. would simply tell you that this "paradox" is simply a thought-experiment, and is intended to be nonsense.

[@sslavi]

This is possibly the longest and the most convoluted presentation of arguments against the figure of Captain Kirk the world has ever seen.

[@jeffdavies2824]

Software engineers call this self referential property "recursion", and in some cases, is hugely powerful (ie calculating numbers to a power, navigating graphs, etc). A for statements that refer to each other, this is "head recursion" or "tail recursion".

[@melkiorwiseman5234]

Welcome to "deadlock"; a known potential problem with recursion. Ye olde GW-BASIC had a "deadlock" error message built into it, but I've never seen it come up. I assume it would only occur when using shared files which have locked records and GW-BASIC is the only version of BASIC I've seen which had the ability to use shared files and locked records, and I've never seen a program which needed to use them (although I did write a prototype "chat" program which used them, just for fun.)

[@xpusostomos]

Any computer programmer knows to be careful with recursion that you exit the loop. This seems like a case of recursive sentences that don't exit their loop. As soon as you refer to yourself, even indirectly via another function, you have to have a plan for when that loop ends

[@Mk101T]

Speaking of computers/software .... which I am only vaguely familiar through game modding software , so pardon my ignorance. But is that why "AND / OR / NOT" are used ? ( logic gates I guess you call them ) Giving 3 options instead of 2 ... and pretty much the idea of truth is somewhat singular in that it is the journeys destination . So false is in a sense taking no journey ? IDK ... but maybe that is how the liar paradox can be solved ... embrace the journey ?

[@nekomikumata]

@@Mk101T it can be solved by a simple inversion truth table. Just take the sentence at face value then invert it. 0 = 1 1 = 0

[@SarthorS]

@@Mk101T AND / OR/ NOT, and others, are used because computers operate on pure logic. Computers cannot perform mathematical calculations directly. They simulate them using logic operations on true and false values. I would give a better explanation, but it's been decades since I studied how CPU's work. Here is an image from Wikipedia that shows the logic gates within a certain CPU used to perform basic arithmetic. upload.wikimedia.org/wikipedia/commons/thumb/c/c0/74181aluschematic.png/600px-74181aluschematic.png

[@mihaichira2888]

In my youth I discovered this paradox, by myself, without knowing about its existence, but in a simpler form: "I lie all the time". I follow your lessons with great pleasure and interest. I applaud you.

[@kennarajora6532]

hey me too.

[@mihaichira2888]

@@kennarajora6532 Nice. :)

[@WWLinkMasterX]

For me it was the episode of SpongeBob where he proposes a "no rules" rule.

[@mihaichira2888]

@@WWLinkMasterX Oh, that's so cool and funny. :)

[@p.kay_____]

Yep me too 😁

[@TheyForgotMySalad]

Your paradox videos tickle my brain in a most pleasurable way.

[@carlcramer9269]

This seems like Gödel's incompleteness theorem - Inside a system you can state a question that the system cannot include (quoted from memory, so go check it up if you are bothered).

[@wcsxwcsx]

First thing I thought of.

[@HowardS185]

Me too - I thought that Dr. Kaplan would mention, or explain more, linking this to Godels Theory

[@HowardS185]

The last work should be theory (damn spelling correction!).

[@Surefire99]

The thing that this and Russel's Paradox leaves out of the equations is the time factor. We live in a world that involves time, so the way we describe things should as well. This problem is evident in programming. It manifests itself in circular logic and infinite loops. That can happen with multiple variables or self-references. But essentially, in order to test something, you need to solve the preceding statement first... which can never happen as you showed at 7:30 in the video. So in programming you could say the solution is "undefined." Another possibility in programming is to pause the loop and test the current state. When you do that, you can't just say "this IS the answer", you'd have to say, "this is the answer at a certain point in time".

[@kennarajora6532]

It's interesting, because your explanation actually bears a lot of similarities to an explanation for the liar paradox made all the way back in the 5th Century AD, by a linguist/philosopher called Bhartrhari.

[@jgunther3398]

a computer is sequential tests and operations, but the"this sentence is false" problem implies at the current point in time. like division by zero; always meaningless. or if a result is demanded for some reason, then "undefined"

[@Surefire99]

@@jgunther3398 the brain is just sequential tests. Things don't make sense if you don't process one word at a time. It might seem instantaneous, but it's not.

[@Surefire99]

@Kenna Rajora just looked into him. Yeah it does seem very similar to what I was thinking.

[@MandoMacDonald]

Right! It’s like “GNU is not Unix”!

[@alonzomuncy6871]

I'm just a programmer buy to me the problem to me seems to be Circular Reference rather than Self-Reference per-se. It would seem to me that if you have some method of terminating a circular reference in your logical system then you can avoid this. I'm pretty sure some smart philosophers have already considered that option, but I have no idea what they came up with or how they managed to restate the problem again.

[@lendrick]

I was going to comment on this as well. It seems obvious enough to me that I'm certain it's already been brought up. I'd be curious how logicians respond to it.

[@jaysoncowan5763]

A programmer has self reference, its called recursion. Recursion that has no action is disposed of by the compiler, because it is indeed nothing.

[@blackshard641]

The beauty of being a programmer when it comes to philosophy is that you work with logic on a regular basis. Programming is applied logic in the same sense that engineering is applied physics.

[@ajb667]

The usual way to deal with circular references is to either ban or ignore them. Given the references are really numbers (i.e. memory pointers or database index ids) you could also wilfully misinterpret the circular references as numbers (change the context) for the sake of something like a serialisation task. I wonder if there's anything from all that we can transfer to this philosophical debate?

[@sandornyemcsok4168]

I am an amateur programmer thus probably I can understand what you try to say. But I can tell you that the problem is not Circular Reference or Self-Reference (i.e. recursive reference). If you read my separate comment I think you will understand where the "cheating" is. 😀

[@w3rkh0f67]

'I am my own oxymoron', or 'Every rule has its exception, even this one..' are some of my favorit quotes. What comes to mind is the Schrödingers Paradox (with the cat in the box) and entanglement in quantum physics. Cool thought provoking video, thanks!

[@SmileyEmoji42]

The Shrodinger's cat thought experiment is not a paradox. The cat really is neither alive nor dead until it is "observed".

[@w3rkh0f67]

@@SmileyEmoji42 Thanks for correcting the terminology. I'm no mathematician, so: as the rules in creation seem valid, until 'observed' (investigated) and then revealing the paradox,- it still strongly reminds me of the Schrödingers two simultaneously valid states.

[@miriam-english]

My favorite is "All sweeping statements are wrong." It's not directly self referential, which I like.

[@w3rkh0f67]

@@miriam-english Haha, yes! Or similar: 47.5% of all statistics are made up on the spot.

[@SmileyEmoji42]

@@miriam-english This is not a paradox, it is wrong. It is not a paradox because being wrong does NOT imply that "All sweeping statements are right" only that "SOME sweeping statements are right" and there is no reason to assume that this is one of those. If you believed it was true THEN you would have a paradox.

[@Lacainam]

I like to think that, while our language (and I mean all language, human language) is incredibly sophisticated, developed, and nuanced, it is only a tool. It is only a way to communicate what is, it does not define what is. It's basically a verbal model that, while well equipped to do what it needs to, is as limited as any model is at describing anything.

[@Joe-nh8eq]

That’s the whole point of the paradox. Our language is just how we communicate reality, its not reality itself. And because of that fact there are inherent quirks and ambiguities in our language which create logical paradoxes. “This sentence is false” isn’t actually a paradox. It’s neither true or false. It’s not real… Which is kind of the whole point of the paradox…

[@ilovepavement1]

For Chomsky it wasnt that thinking was a result of language, but that language taught us how to think.

[@michaelw7115]

I think it's both, and anyone who knows 2 or more languages pretty well will testify to that. The better your grasp of language the deeper you can develop thought but deep thought can also reveal a lack of words in a language (which can end up affecting whole societies and cultures unaware of the existence of such words known in other languages. @@ilovepavement1

[@petermcminn9508]

Exactly. Our shared understanding of the "sentence", a construct in itself, presents a mobius strip of a kind, a flawed vehicle we use to navigate our universe: if-this-then-this in perpetuity. @@Joe-nh8eq

[@paulpease8254]

Thank you Professor Kaplan! Watching your videos has rekindled my love of philosophy and academia. Cheers!

[@bradr3541]

“This sentence is partially true.”

[@tonyduff-forbes5748]

My father was a senior university lecturer in philosophy, his area was logic, and mathematical philosophy, great video!

[@seijirou302]

A thought that came to me while watching this is that it sounds a lot like Gödel's Incompleteness Theorems. It seems to me that language can be replaced with mathematics, as Gödel did for symbols. In the same way that Gödel used this system to prove that mathematics can not be complete and consistent, it proves also that language can not be complete and consistent. As language is a fundamental constituent of formal logic (I know, I'm probably recklessly asserting here) it follows that formal logic can not be complete and consistent. Or perhaps a way out is to say that logic may be complete and consistent but the expression of logic can not be.

[@marcvanleeuwen5986]

While it is true that the Russell paradox arises from self-reference, it does not arise simply because a set can be an element of itself: there are consistent set theories where this is allowed. The contradiction comes from allowing a set to be defined by selecting (by a predicate) items from a universe to which the to-be-defined set itself belongs. Similarly the liar paradox arises from allowing the meaning of a sentence to depend on the assignment of truth values to collection of sentences to which the sentence itself is supposed to belong.

[@vorpal22]

@@CorwinSTP No, we just learned what constitutes a logically consistent entity, and we refined our definitions to call those sets. Clearly, derivations of properties of inconsistent entities that are set-like fall apart, so it is important to make the distinction. There's no cherry picking involved.

[@njsmeets66]

This is why we created or invented the "paradox."

[@Bronco541]

@@CorwinSTP it seems to me like most people are unwilling to accept that this whole thing represents a limitation of our present brain power; or our modus operandi to which we perceive/create the universe.

[@marcvanleeuwen5986]

​@@CorwinSTP The Russell paradox arises in a _formalization_ of naïve set theory. As an informal theory, naïve set theory only informally describes what sets are, how they behave, and what one can do with them (like take intersections of them, form sets of sets). For instance, while Georg Cantor definitely meant to study infinite (as well as finite) sets, I doubt whether he actually stated a clear rule that some infinite set exists (and without such a rule, one cannot _prove_ that any infinite sets exist; indeed Greek philosophers held that nothing can possess actual infinity, as an infinite set would, and this is a logically consistent point of view). So if one wants to do rigorous mathematical reasoning about sets, one needs to fix the rules, i.e., formulate axioms of set theory. Gottlob Frege undertook such a formalization (maybe not exactly of Cantor's set theory, but something essentially equivalent). The set of rules must be proposed; there is no (cherry-)picking from a pre-existent set of rules involved. The main things that formalized naive set theory proposes about sets involves equality of sets (two sets are equal if anything is member of the first if and only it is member of the second) and an axiom about sets that (must) exist; for the latter it states that any well formed predicate (in the language of set theory) defines a set (of everything that satisfies the predicate). This is elegant and economical (for instance one does not need to state explicitly, as starting point, that an empty set exists, since the predicate that is always false "creates" the empty set; similarly, the predicate that is always true creates a universal set, as set of which everything is member. Unfortunately this elegant axiom also make the theory inconsistent, as Bertrand Russell pointed out to Frege. (Incidentally, the inconsistency arises by applying Cantor's theorem, stating that every set has strictly smaller cardinal than the set of all its subsets, to the universal set; no great originality on the part of Russell was required.) So nowadays we use a formalization of set theory (usually the ZFC axioms), in which the naive rule for "creating" sets is replaced by several axioms that state that certain sets exist. One for instance states explicitly that an empty set exists, another that some infinite set exists, and ZFC has some other existence axioms. Most relevant here is that instead of "naïve comprehension" mentioned above it has "restricted comprehension", stating that for any set X and predicate P one can form the set (subset of X) of all x in X for which P(x) holds. The fact that an explicit (already existing, in a sense) set X must be supplied, instead of implicitly selecting from the universal set as in the naïve theory, avoids Russell's paradox in ZFC. This is what I meant by "The contradiction comes from allowing a set to be defined by selecting (by a predicate) items from a universe to which the to-be-defined set itself belongs".

[@njsmeets66]

Excellent! Much appreciated, thanks!

[@seniukas]

Thanks for keeping us sane, professor. You are the paradox guy, always fascinating to watch.

[@zambo6453]

my personal favourite application of this is from portal 2. giving as few spoliers as possible, an AI is displaced from running a facility by another AI which is specifically designed to be an imbecile (there is a sensible in-universe reason to design such a thing...kind of) so the first AI plots to retake the facility by destorying the second with this paradox (while turning off its mic so it can't hear what it is saying, and therefore destroy itself). The AI hears the paradox, thinks for a second and says "hmmmm. I'm gonna go with.... false. Did I get it right?"

[@Downhuman74]

I always loved this part of the game. GlaDos doesn't seem to know that even her knowing about the liar's paradox is, itself, a paradox. Just merely knowing and understanding the paradox and what it apparently does to a being of pure logic should destroy her as well based on her understanding of it (which means it shouldn't matter if she hears it or not.) But it doesn't destroy Wheatley, just like it doesn't destroy her. Man, there are just layers upon layers to that whole exchange.

[@flecko5]

It's not necessarily a paradox for her to know that she shouldn't use it on herself. All she really needs to know is that it'll break her circuits if she thinks about it.

[@devonadler5835]

a fantastic book on self reference and metamathematics comes to mind- "Godel Escher Bach, the eternal golden braid" where the author talks about some of the similarities and paradoxes involving metamathematics, the impossible architectures of escher, and the melodies of back

[@nosuchthing8]

That book rules

[@lorefox201]

it rules so much

[@impyre2513]

Seems to me that the problem is the combination of implication and circular reference... I mean, if you ever dig into how implication works it seems obvious that circular references using them would be inherently problematic (since they are *not* bidirectional)

[@matteritchie]

Just started watching some of the Jurisprudence lectures because I wanted to become more conversant in the field, and - wow - I really love these lectures...just about all of them I've sampled. Thanks for sharing them!

[@trishoconnor2169]

There must be something in the way my neurons are wired that makes me simply reject most "logical paradoxes." For this particular one, my intuitive response has always been something along the lines of "Irresolvable loops (no matter how many steps you try to put in them) have no meaning." It's kind of like the error message a spreadsheet will give you if you try to divide by zero, just a simple, "Nope, that can't be done, so do something else instead." It just seems so obvious to me that this is the answer that I don't understand the effort expended on it over the centuries. Intellectually, I realize that brilliant thinkers have been fascinated by it since at least 400 AD, so I know it's not actually stupid, but this awareness does not keep my personal reaction from being, "That is just stupid." Same with Zeno's Paradox: No, it's not paradoxical to try to walk from Point A to Point B because you have to walk half the distance, then half of that distance, ad infinitum, so you never get to B. I don't intuitively "get" the paradox because we DON'T walk by halves. Period. That's just not how it works. This has left me feeling quite free to move on with my life, and clearly would have made it impossible for me to make a living as an academic logician.

[@CodeguruX]

Language is a man made construct. Assuming there is no fault in a manmade construct is false.

[@trishoconnor2169]

@@CodeguruX That statement is true.

[@tanjirouzumaki444]

Actually, we could potentially “walk by halves” depending on your definition. The only reason the paradox is false is because infinite sums don’t produce infinite values.

[@iangreising9057]

Oh, something shiny. . .lol

[@0x7f16]

A thought on the circular reference problem in the video: If we formalize the sentences (a) The sentence below is false (b) The sentence above is true as follows X := ~Y Y := X (where := means “is defined as”) then substitute the second sentence, which is the definition of Y, into the first sentence, and we have X := ~X which is the same as the liar’s paradox: X occurs in the definition of X itself. Therefore it will be an infinite loop if we substitute X’s definition for X in X’s definition. I think it’s a problem with circular definition - a name that contains itself in its definition. Thus when we try to expand it, it will end up in an infinite loop. So can we just ban circular definition to avoid the problem?

[@0x7f16]

I’m thinking of a macro-language compiler that substitutes every name in a sentence with its definition (except for the primitives). In order for the compiler to finish in finite time, at any point of expansion, it should not be the case that a name occurs in its own definition (which is a thing we can test for, say, write a program for it).

[@NemisCassander]

Banning circular definition is, essentially, removing self-reference. Kaplan sort of says you can avoid self-reference, but it's really just hiding it. The issue is with series of statements whose _entire_ definition relies on other terms. Statistically, you can say that the system of circular definitions you give have zero degrees of freedom, which means the error cannot be measured. Ergo, the truth cannot be determined in such a system.

[@lasarila1629]

Interesting idea. ChatGPT could probably help you expand on it if you wanted to test it quickly. Good luck!

[@camelCased]

Well, the problem is that you cannot ban something from existence if it exists :) So we cannot ban circular definitions "just because". Also, there are practical real-life situations when we have to deal with circular references - it's when serializing a parent-child data model where they both reference each other. The developers of serializers implemented different tricks to deal with this, but they could not "ban" it.

[@hihoktf]

I don't think circular definition in and of itself is the problem i.e. X:=~Y Y:=~X is circular, but is always true and without paradox. I think it's self-referential denial (whether immediate or mediated), which is what you presented, that is the failure mode of the liar's paradox.

[@prischm5462]

The book "Gödel, Escher, Bach: An Eternal Golden Braid" by Douglas R. Hofstadter also explores this in great detail. It can also be expressed by the Quine sentence: "'Yields falsehood when preceded by its quotation', yields falsehood when preceded by its quotation."

[@Rot8erConeX]

GEB:EGB mention nice

[@santaclaus0815]

Hats off to Ethan! He kept Jeffrey from telling us things about the liar's paradox that aren't true - or worse - neither true nor false.

[@iangreising9057]

Lololololol

[@Akari-br7ci]

I've heard of this paradox before, I think most of us have, but I've never really thought about it that much. I just went "that's kind of cute" and move on. I never realized how many variations there were and all the implications they have. Really great video.

[@flygawnebardoflight]

My favorite thing about "this sentence is false" is that if you declare that it is paradoxical then it becomes true as it isn't false, breaking that paradox and creating a new one.

[@benjaminshropshire2900]

To me, the resolution to the paradox is simple; the world is under no obligation to make every possible statement self consistent or even meaningful. The fact that a statement is neither true nor false is interesting (mostly in what it says about the language the statement is made in), but not at all surprising. In fact, the non-existence of such statements would be the surprising thing.

[@BabaJeez]

@@benjaminshropshire2900 Agreed, and I would go even further. A statement can NEVER equate to absolute truth or absolute falsehood, since words have no precise meaning, being sounds or markings that trigger memories of experiences, not having any fixed meaning. This even includes mathematical statements such as 1+1=2, because numbers have no actual meaning until assigned to represent something (e.g. 1 apple + 1 apple = 2 apples).

[@benjaminshropshire2900]

@@BabaJeez I wouldn't go that far. Words have precise meaning, at least to the extent the people using them agree on what they mean. And societal discourse depends on having wide agreement on that. Where things get strange is when one side of a debate tries to win by trying to choose the meaning of terms the other side already used and then say that is what the other side meant. The problem there is that changing the meaning of words doesn't change the meanings people are expressing. At best it just pisses off the people trying to talk about something. At worst it tricks the other side into thinking they succeeded making it impossible to resolve anything in a civil way.

[@BabaJeez]

​@@benjaminshropshire2900 What I meant is words never have *absolutely* precise meaning (to speak of relative precision in this context doesn't make sense). A statement can never be absolutely true or absolutely false. One could argue a mathematical statement can, but I would again point out that math has no actual meaning when the numbers are isolated (i.e. when they aren't representing anything "real"), and that always includes concepts with no absolutely precise meaning. What is the average airspeed of an unladen swallow? What do you mean? African or European swallow?

[@benjaminshropshire2900]

@@BabaJeez your clarification is saying what I already understood your original statement to say. I still disagree with both.

[@johnyork5121]

I feel like a sentence cannot be self aware and a pair of sentences cannot be self aware or aware of each other. Love the star trek references

[@daniellehallihan6015]

You're a really great teacher. You go through each point slowly and clearly and give us plebes the time to process what you're saying. I've watched Russell's Paradox and this one, the Liar Paradox, and I'm just blown away by your ability to break things down and explain complicated, mind-bending ideas. Also, you're funny 🤭 and have the hot professor thing going on. Soooo... I'm definitely subscribing. 😂🔥

[@dannyzwolf4546]

The solution to the paradox is simple. The sentence "this sentence is not true." Is that it's self contradictory. It doesn't matter if it's ture false or otherwise.

[@Stroheim333]

The Liar's Paradox, and all of it's variations in the video, is dependent on pure semantics, and the only thing the paradox prove is that pure semantics is not, and cannot be, perfect or consistent. Semantics is NOT reality, it is just a tool for us to communicate reality (or fantasies, or nonsense, if we want to).

[@jeremypnet]

The two sentence version is still self referential. I prefer the Quine version (which is where I thought you were going with the infinite fribbles). This goes something like this: “Is false when preceded by its quotation” is false when preceded by its quotation. This is a sentence that tells you how to construct a new sentence from a sentence fragment. It also gives you a property of the newly constructed sentence I.e. that it is false. If you follow the instructions, you happen to get the same sentence back. It’s self referential without referring to itself.

[@va3ngc]

I think the solution is still about self reference ending up being a form of recursion. In the two sentence version, when you have one sentence pointing to the other, you end up with the recursion problem again.

[@georgelionon9050]

Exactly, but "there will be a surprise test tomorrow" has absolutely no reference and still gets a similar self contradicationary cycle (there cannot be an announced surprise, but once the sentence is considered absurd it is true because it will be a surprise)

[@nickmarras249]

A classic case of overthinking. And THIS sentence….is TRUE!!!

[@ShimulHasan-c8p]

😂

[@explodingpotato6448]

The way I always thought of this sentence is for a sentence to be true or false there has to be a way to evaluate it, in this case there is isn't, so you have to first assume that it is true or false for the paradox to begin.

[@irrelevant_noob]

Precisely. There are sentences for which no truth value can be assigned. 👌

[@love-wisdom]

Will you ever do a whole video dedicated on how to use logic and logic tables?

[@morgoth5460]

you might want to try out the following playlists if your interested in logic and logic tables: kzbin.info/aero/PLqEJ_rxb3Xf1l1KbR33vNyjAqwg8Adq8K kzbin.info/aero/PLKI1h_nAkaQq5MDWlKXu0jeZmLDt-51on The first one is more philosophy oriented and is taught by David Agler (a phil assistant professor) and the second playlist is more general and taught by William spaniel, an assistant professor from a political science department (doesn't use standard philosophy of logic syntax, which can make it a bit easier for beginners, but this is not so useful later on at an advanced level)

[@SilverBullet93GT]

This video does not exist

[@DG123z]

This comment does not exist

[@youinfosucker8887]

This comment is false

[@LocStoriesbySilver]

Your comment is false Meaning my comment is true

[@trucid2]

That's not a paradox. That's just a false statement.

[@butter5144]

True/false

[@tycarlisle7436]

Here is my theory. Answer to the Liar Paradox Temporal Properties Take for example “The King’s Apple Decree” A King in Normandie France needs apples for the upcoming calvados festival. “The King hereby decrees that His Majesty shall own every 10th apple owned by peasants of His Majesty's Kingdom.” Consider the example of a peasant named Jean Dupont, who resides in the Kingdom in question, and whom only owns a single young apple tree. And, furthermore, let us consider the scenario where Jean Dupont’s young apple tree happens to only produce 10 apples. Now consider the following sentence in reference to the aforementioned peasant: “Jean Dupont owns 10 apples.” Can this sentence be true? After all, the King, who has sovereign right over all the apples produced in his Kingdom, has declared that he owns every tenth apple. Therefore, one may think, it should not be possible for Jean Dupont to own 10 apples, unless he actually harvested 11 apples. However this logical fallacy presupposes that it is impossible for a peasant in the Kingdom in question to own a 10th apple. Therefore, even if Jean Dupont harvested 1 million apples, he would still only own 9 apples, because every 10th apple would belong to the King. It would be impossible for a peasant in this Kingdom to own a 10th apple, and therefore the King would own every apple harvested after number 9. However, this fallacy also makes it impossible for the King to ever own even a single apple. Since it is impossible for a peasant in this Kingdom to own a 10th apple, the King can never take ownership of any of the apples. In this interpretation of the scenario, every apple after 9 would fall into an ownership gray-area where they are neither owned by the peasants, nor owned by the King. This fallacy can be avoided by the idea of temporal ownership, or by applying “temporal properties” to true or false statements. “Jean Dupont owns 10 apples” can be temporarily true. Under modern bankruptcy laws, this scenario happens all the time, whereby money or property which comes into the ownership of a debtor is passed on to the debtee, once the bankrupt party comes into possession of the assets in question. Considering this idea of “temporal properties”, let us re-examine the strengthened liar paradox. “The meaning of this sentence is not true”, in my argument, can be temporarily untrue. However, once the sentence becomes untrue, then it will be a true sentence. There is no paradox here under the idea of “temporal properties”, since there is an understanding that any properties given to an object or idea can change over time. IN FACT, it would be impossible for the above sentence to be both true and false at the same time, since the sentence would only become true after first being false, and vice versa. This can be further understood by comparing it to Hermann Minkowski’s principles of spacetime, first posited in 1908, and later expanded upon by Albert Einstein. Under modern physics’ understanding of space and time, neither can exist outside of one another. For instance, if you were to tell someone that you would like to have a business meeting with them, it would not be enough to say “We are having the meeting in New York City”. You would need to tell them the x and y coordinates (e.g. the Flatiron Building at the corner of 5th avenue and West 22nd Street). Then you would need to tell them the z coordinates (our offices are on the 7th floor), then you would have to tell them what time (e.g. Jan 1st, 2025 at 8am Eastern Standard Time). The x, y, z, and time coordinates in this example, are properties of the meeting, in this case “where/when the meeting took place”. In a similar manner, I would propose that no property of an object or idea has meaning without a temporal component to that property. We all innately understand the temporal components of properties, as they are always baked-in to our language. This is natural law. The sentence “Jean Dupont owns 10 apples” already answers the question of when he owns the 10 apples. The answer is “right now”. The question of how soon the 10th apple passes ownership to the King, and, similarly, how long “right now” lasts, is an esoteric one, and meaningless for the above discussion. The only thing we need to presuppose is that “right now” does exist in some form. Following from this, “Jean Dupont owns 10 apples” was true at the time at which it was conceived. Therefore “The meaning of this sentence is not true” can be untrue right now. That the sentence then becomes true, does not change the fact that it was untrue in the moment it was conceived, anymore than you can say it is impossible for Jean Dupont to ever own 10 apples. Edited Jun 20 2024 at 6:25am PDT (clarified a few words and phrases)

[@richardmeyer3214]

Responsibility is not the only trait needed to be a captain! Kirk was bold and that's important. Solid video tho

[@bernardoohigginsvevo2974]

William Shatner the bed.

[@fisyr]

Frankly I think Kirk should have been the chief of security and Spock the captain. Since Starfleet always insists on not being a military organization, it'd make much more sense to have a more diplomacy/science oriented leader in that position. But I don't know why I'm discussing that in a video about logic. ^^

[@TheSwiftCreek2]

He was also more likely to sacrifice himself than Jean-Luc.

[@ruprecht9997]

Jean Luc was bald too.

[@ruprecht9997]

@@TheSwiftCreek2 It was quite hard for Kirk to sacrifice Jean-Luc given that they lived in different eras! ;-) I know they overlapped a few times, but still I had to make this important point. Heh heh.

[@psifiusc]

Like Zeno’s paradoxes and the end consequence of much in philosophy, the value of the Liar’s Paradox seems to be the lesson we don’t want to accept: even at its best the human capacity for reason and comprehension hits a limit pretty early on. The actual point seems to me to recognize that we’re a much less clever species than we pat ourselves on the back deluding ourselves to imagine. Logic is likely as good as we can do but as we designed it, it’s still embarrassingly flimsy.

[@Zebulization]

Or the liars paradox is a collection of words that have been arranged according to grammatical rules, but which actually have no meaning. Such as: The invisible pink unicorn. Just because concepts can be shoved together doesn't mean that they will have meaning once they are put into the same arbitrary container.

[@fluffysheap]

On the contrary - the problem is inherent to logic, and it's only human cleverness that lets us see outside the logic box and actually solve the problem (Godel's Incompleteness Theorem).

[@leslieviljoen]

These videos are fantastic. Thanks so much for putting them up!

[@GoingToBeWild]

These sentences break the chain of causality, the use of a statement before it is defined, which causes an implied recursive reference and results in a paradox. "This sentence is false" refers to itself with the word "this". "The sentence below is false, The sentence above is true" the first sentence refers to the 2nd sentence before it is defined. Russell's paradox also breaks causality, "The set of all sets that does not contain itself"... it could not contain itself until after it is defined, the use of the words "all sets" is recursive

[@Clumbob]

The paradox results from infinite recursion, not self reference, right? "This sentence is 30 characters long" is self referential but not paradoxical. Changing from one to two sentences that reference each other still results in infinitely long sentences when you replace "the sentence above/below" with the sentence that phrase is a stand-in for.

[@kennarajora6532]

It actually reminds me a bit of Thomson's lamp.

[@irrelevant_noob]

*35. Spaces are characters. ;-) But even if we grant you that it's not "any kind of" self-reference that is the issue, only infinitely recursing ones; how can we decide whether some given self-ref is infinitely recursing or not? The halting problem isn't solvable... :-| PS You're correct that the 2-sentence alternative goes into the same infinitely-recursive box, but it was presented as a way to bypass the SELF-referential nature of the paradox, not the infinitely-circular nature.

[@robertashton8942]

Hi Jeff. Your paradox explanations and analysis are the best of all the paradox videos on KZbin. Thank you so very much for this great work. I have become your fan instantly.

[@kakyoin3856]

The paradox reminds me instantly of XOR logic gates. It negates the output after both inputs aren't equal. It is funny how the paradox works with its "logic".

[@plazmica0323]

that makes it a valid third option

[@benheideveld4617]

The problem lies with referencing. According to Aristotle in his essay “On Interpretation” the requirement of a proposition is that it needs both a subject and a predicate. Kaplan erroneously uses the word sentence, but a sentence does not need to be true or false, a proposition in ordinary logic must be either true or false, but that doesn’t mean you can know if it is true or false. There are other tricks too, like “The final digit of π in decimal representation is unknown.” In order for this sentence to be a proposition, “The final digit of π in decimal representation” pretends to be the subject. But we all know that π has no final digit, because its decimal expansion is unending. Therefore the phrase purporting to describe the subject is describing an impossibility, therefore the purported subject is invalid as a subject. Therefore the sentence lacks a subject. Therefore according to Aristotle the sentence isn’t a proposition. Therefore the sentence cannot have a truth value. A subject containing a reference that does not completely materialize, here meaning lose all referencing elements after a finite number of substitutions, just isn’t a valid subject and without subject we don’t have a proposition and a sentence that isn’t a proposition cannot have a truth value and hence cannot yield a paradox.

[@markoates9057]

I agree here. Processing the statement "This sentence is false" also requires a parser of sorts. I don't see a paradox in the statement, rather a misinterpretation (and perhaps blind trust) that the parser of the sentence behaves in a way that it does not. A trivial example: a 5 year old kid is running around the room saying "This statement is false lol". Obviously a "language parser" for this context would be a little wiser than simply being flung into an infinite recursion and deadlock. It would discard the sentence as nonsense and invalid.

[@wandabadenhorst]

The sentence in question is neither True nor False. It is simply a sentence. To test it's truth or falsity you would need to know what "Truth" is, and according to the paradoxical nature of Epistemology this enquiry is not possible (lol)

[@headhunter1945]

The liar's paradox seems something like expecting to be able to say what color the animal was from the sentence "An animal swam in a lake." Maybe there is a correct answer, but it does not yet arise from the given premise. Or perhaps a better simile would be "How does the food of an empty bowl taste," "What is the sound of one hand clapping," etc.

[@irrelevant_noob]

But what's the premise which is insufficient to get to that "correct answer"?! Also, in your "how does non-existent food taste" example, i think any answer would be valid, since in logic, false premises can imply anything.

[@johnmartin5671]

"I always lie" is an alternative way of expressing the liar paradox.

[@ShredPile]

And a better one I think. It feels like the other examples could be argued from a grammatical stand point.

[@johnmartin5671]

@@ShredPile Thank you!

[@buycraft911miner2]

Its not really. The sentence is false -> I always lie is false This doesnt mean "I never lie", it means "I dont always lie" so you can still sometimes lie, you just dont do it always

[@irrelevant_noob]

@@ShredPile how is it better if it's incorrect? :-)

[@nigeldepledge3790]

Erm . . . but isn't it the case that we can always construct self-contradictory statements in any language-based system? We're often told that there are no stupid questions, but I find it easy to construct a stupid question by subverting the rules of language. (I use the example "What is the difference between a duck?" to illustrate how easily we can make a stupid question when we put our minds to it.)

[@lazarushernandez5827]

When read, the question seems incomplete because the words 'difference' and 'between' infer that 2 or more things are going to be compared. In the right context, the question can be understood as, what is the difference between 'any' duck? As in the person asking that question does not perceive any appreciable difference (to them) between one duck and the next. For example replace duck with soda. What is the difference between a soda? The person asking this question may be talking about sodas in general and lacks a preference for one particular brand.

[@mattrothe149]

A duck has no between the toes because it's full of webbing. Wow, it's been a long time! Does anyone else remember this?

[@Eyeballsandwich]

Of course, the well known answer to this is, “one of its legs is both the same”. Ask a stupid question…

[@stevehaire6324]

I have never before learnt so much about a subject but ended up knowing the exact same amount about it as I did prior to learning it. How's that for a paradox.

[@a.hardin620]

Shatner is definitely suing you. Be prepared! 😃

[@rickboucher5419]

Except that Shatner is objectively a worse actor than Stewart.

[@xtieburn]

I always get caught up in a similar issue with many of these types of examples, which is that they seem to make a huge leap between semantics and logic. We already know language isnt logical so it doesnt seem that surprising that you can form logic breaking sentences. So it seems that youd have to prove that these specific sentences are an accurate representation of something more fundamental. Its much the same with the Russells Paradox video, perhaps its just for brevity, something thatd take too long or be too boring to cover in a KZbin video, but there always seems to be this odd jump, despite it being quite clear you cant do that, that our language is not even close to being some ideal system you can analyse in perfectly logical terms.

[@MikeyDavis]

You spittin fire Bob, couldn’t have put it better myself.

[@stuartzekaj1423]

I wouldn't exactly know how to construct a satisfactory argument against what you just said, but my immediate thought is that the jump was always there to begin with. To create a logical system you necessarily need some form of signification, a language is at some point formed (an interconnected system of signs and signifiers) which gives rise to semantics within the very form of logic itself. It seems that there is no way (from our human perspective) to come up with a logical system without first having a language to base it on. My idea here being that you are fixated on a "leap", which perhaps can only be observed after initially ignoring an original "leap" from language that gave rise to the logical systems you are now thinking about. Although I''m genuinely interested to know what you mean exactly by "language isn't logical".

[@101Mant]

We use language for convenience but you can express the same things with the same paradox in formal logic. So it cannot be an issue with language but the underlying concepts.

[@davidhoekstra4620]

@@101Mant Methinks formal logic is itself a language. It seems to me language is a way to deal with reality symbolically because this simplifies life. These paradoxes might be telling us that there is no perfect way to do this. Nevertheless language is so useful that we must resort to it despite it's imperfections.

[@ZephonOrion]

So is there really anything to believe what's been said in this video?? What if it's all a lie too?? 🤔😳

[@ivok9846]

something was said? first minute and a half was looping paradoxes...

[@poeticandroid]

That's up to you cause all we are our perception and know. If one believes god exists you cannot prove that wrong. You can only prove things can be proven.

[@ivok9846]

@@poeticandroid why not? present him with following: assume we have 2 worlds, one with God, other without: what's the difference? will he come up with good answer? (I didn't include 'she' as they don't seem to like philosophy)

[@DeathScyther006]

This video is the cake

[@poeticandroid]

@@ivok9846 Sorry but I am quite lost on this one. Only if you can elaborate a Lil.

[@MacWiedijk]

The point is that there are two things that don't necessarily match. The first is the content of a statement and the second is the status of the content of the statement. In “this sentence” the content is referred to as the statement, but not the status of that content. The statement is false because that is the content of the statement. But if the content of the statement is false, that makes the status of the statement true. “This sentence is false.” is therefore true.

[@Aim54Delta]

As I always found amusing in elementary school: "Today is opposite day." And, thus, the universe imploded. There is an interesting experiment in QM that might be interesting in this context, called "The Quantum Bomb Detector." Effectively, by doing some clever things with splitters and wave functions, you can build a detector that tells you about something that didn't happen. It could point to our mathematical sense of logic being partially flawed or incomplete. There again... using QM to try and answer philosophical questions is about like using philosophy to answer QM questions and we are left with an existential crisis as we can't answer whether or not the moon is there when we aren't looking (to take the problem to hyperbole as Einstein did).

[@camelCased]

That led me to an amusing question - are were "here" when we are not aware of ourselves (e.g. sleeping)?

[@DarkVeghetta]

@@camelCased It's entirely possible the answer could be 'no', if we're actually a type of simulation. It would resolve many fundamental problems with reality. @OP I would argue that, similarly to QM, there are more than two logically achievable states. Specifically: true, false, and recursive (which is, ultimately, just another word for 'paradox' - but it just might be the only method of addressing the issue).

[@camelCased]

@@DarkVeghetta Yeah, it feels like Schrodinger's cat - it's both true and false, until you open the box (stop recursing) and do the measurement.

[@fluffysheap]

There are great videos on the quantum bomb experiment by Sabine Hossenfelder and PBS Spacetime. It's a completely different weird thing than this, but they are both weird!

[@Aim54Delta]

@@DarkVeghetta Is there really a third state, or is it simply our inability to perceive reality which creates the appearance of two distinct states? For example, asking whether something is a particle or a wave results in the conclusion it is somehow both... which is weird only because we are using our perception of reality and mathematical tools of prediction to describe the behaviors of something which does not necessarily have to conform to either. There is a very interesting work, a manga, called "Dead Dead Demon's Dededededestruction" - it's a sort of modern Gulliver's Travels in a sense and mostly a social critique - but there is an interesting sci-fi premise as it pertains to the perception of reality. It also falls into the "deathworld" and "humans are space orcs" category. A sort of fusion of the anthropic principle wherein we don't necessarily create reality, but our imperfect perception/grasp of what is truly occurring has a consequence for how that reality is experienced. Consider how easy it is for us to talk about a subject in the abstract. If I come up and start describing a set of directions for how to get somewhere, you can couple the use of sounds and symbols to the abstract ideas of things that are not within your perception at the moment. I can describe a building or set of landscape features that you can understand as something not currently present. Now consider the perspective of a dog. You come up to it and start saying things. It might recognize the word grass... or tree... but clearly, you're being silly, as neither such thing is present. Or maybe you're telling it you intend to go outside? The capacity of a dog to formulate abstract concepts is extremely small relative to people. They are obviously not without intelligence, but the multiple layers of reasoning to create language, that are second nature to us, are completely alien to anything a dog understands. Likewise, perhaps our inability to resolve these challenges is a similar mental block and with more capacity to process information, it would become obvious to us. I kind of suspect we are smart enough that, given enough time, we can reason through any problem - but there again, the chasm between 140 IQ children and 110 IQ children would indicate that there may be hurdles that can only be cleared through improved baseline performance. ..... of course, behavioral disorders and the like among high IQ examples kind of draw into question whether or not that would hold true..... i am rambling at this point.

[@alphax4785]

The thing that bothers me about equating the two sentences referring to each other with the self referential sentence is that the two sentences are still two sentences, so when you're reading the one its statement is the controlling one and then when you read the other its statement would be controlling. It's like a 'useless box' that when you flip a switch to on it flips the switch off, there are two actors, you turning the switch on and then the box turning it off. Yes, that is 'useless' but not a paradox.

[@MichaelAnderson-ir7hz]

Kirk is a(n amazing) soldier. Picard is a(n amazing) diplomat.

[@philwaters9751]

At last a decent answer to the only real debate in this debate... xxx ;-)

[@mmmk6322]

Question in the dismissal of the self refence using two sentences. Is it not that the two sentences would lose meaning if they were written without being underneath/above the other sentence? Doesn't that just make it back to a case of self-reference with that addition that the refence entails that both sentences reference each other, making them a self-reference paragraph/unit.

[@linsqopiring6816]

Bruh, you were doing so well. This is the second video of yours I've seen after Russel's Paradox and was loving this one as well. Right up to the instant where you wrote "The sentence below is false" and claimed you had avoided self reference. Are you kidding me? I'm dumber than the gum on your shoe but even I can see that you didn't do that because "The sentence below is false" is clearly a shorter way to say "The sentence below THIS ONE is false". The sentence below what is false? The sentence below THIS ONE. So it becomes "The sentence below 'The sentence below is false' is false" recursive to infinity. Not sure how you could miss that.

[@Mitchell_is_smart._You2bs_dumb]

it could have easily referred to the space occupied by "this one" the sentence on line one says _"the sentence on line 2 is false"_ the sentence on line two says _" __-this was a good video and not just a steaming pile of crap intended to harvest view time-__ the sentence on line one is true"_

[@linsqopiring6816]

@@Mitchell_is_smart._You2bs_dumb I agree. It *could* have. Which makes it all the more surprising he didn't do it that way. It's a glaring error with an easy fix. But I also agree with your redaction so I guess I'll give him another chance.

[@maxwellschmidt235]

Great review of Spock's character. One theme of TOS is that logic is valuable, but that logic cannot capture the totality of experience. Logic should be our closest advisor but it should not overtake our human ability to empathize.

[@abergdahl]

I think the solution is quite simpe actually. "is true" and "is false" are used to evaluate propositions, claims of some kind. Like "it rains" so to use the phrase " is true " or "is false" is only meaningful in order to evaluate a claim or proposition. A way to think is that we reduce away all "is true" or "is false" and see if there is a freestanding claim,. "it rains is true" is reduced to "it rains" which is a claim "it rains is false" reduces to another claim. However if we take "this sentence is false" and reduce it to "this sentence" we do not have a proper claim or proposition. The same evaluation comes into claim with "fetch me some water" is not a claim it is not true or false Searle discuss such sentences in depth and state that they have "conditions of satisfaction" by stating "fetch some water" it becomes satisfied if someone brings me water but it is not true or false. So the conclusion becomes that "is true" and "is false" are operations on propositions i propose that "it rains" and there fore it can be true or false. If i write out "It rains is true" it says no more that the original sentence "it rains" . "it rains" i true if, and only if it rains. "it rains is true" is true if, and only if it rains. "this sentence" is neither true or false and if we reduce "this sentence is false" to "this sentence" we see that adding "is false" is simple a mistake because it is not added to a proper proposition. The answer then is "this sentence" is not a P and only a P can be true or false"🤓

[@DonkeyPunchAllstars]

I stumbled on your videos for the subject matter, I stayed for your suburb analysis of Star Trek captains.

[@starroger]

Seems to me, comparing Star Trek captains just within the context of their particular shows without also considering the popular culture of the time these shows were produced is an offshoot of the 'self-reference' problem. There is a 30 year lag between TOS and TNG. Cultural attitudes regarding women changed somewhat over that time.

[@AriaHarmony]

That's the thing about recursion: to understand recursion, you must first understand recursion. It's funny that in philosophy this is just a paradox, but it's used directly in programming. As long as you put a limit on how many times you repeat yourself, otherwise your code will crash. So recursion is where you really start making mistakes as an amateur, because initially it's hard to wrap your head around a function that keeps calling itself that keeps calling itself that keeps calling Itself that keeps calling itself that keeps calling itself that keeps calling itself that keeps calling itself that keeps calling itself that keeps calling itself that keeps calling itself that keeps calling itself that keeps calling itself that keeps calling itself error maximum recursion depth exceeded.

[@Tijuanabill]

It's confusing because Kirk was clearly a better captain. His mission was not to keep the crew alive; his mission was to seek out new life, and boldly go where no man has gone before. Picard's mission was not the same mission; he is dealing with established diplomatic conditions. His decisions are much more clear because he doesn't have to think creatively, in the moment.

[@valedictorianism]

I was fascinated by how absurd the liar paradox was, up to the point when you said that that French (or Canadian, or whatever) baldie is a better captain than old Kirk. You shot yourself in the foot there, because the absurdity of the paradox got immediately deflated. It just paled in comparison. Now you owe us a video explaining a much more absurd statement.

[@OgamiItto70]

He thinks Picard was a better Captain than Kirk because Picard is visibly bald. Birds of a feather. Or lack thereof.

[@valedictorianism]

@@OgamiItto70 , your logic is flawless.

[@OgamiItto70]

@@valedictorianism Sauce for the goose, Mr. Valedictorianism.

[@wswanberg]

It can be measurably and reliably demonstrated that Kirk was the better captain.

[@valedictorianism]

I concur.

[@spirosxania3745]

Hello! I've recently discovered your channel and i loved it! I have a question about this video which could be kinda silly but i couldn't answer it and would like some help. Just before this video i watched your video on Plato's Euthyphro in which you mentioned the example with the greenness of the grass and the trueness of the sentence (the grass is green) and how the first explains the second and not the other way around. In 1:10 in this video you stated that "if the sentence is true then the ship is on fire". So my question is: shouldn't the fact (sentence) that the ship was on fire explain the trueness of the sentence "this sentence is true" and not the other way around? If its the other way around (being parallel to god saying that murder is virtuous in your Euthyphro video) that would mean that if the sentence was for example that murder was virtuous that would mean that it would actually be virtuous because the sentence above said that the sentence (below) is correct. I hope you read this and keep up the good job!

[@Anonymous-ru9jv]

this comment is false

[@throwaway692]

And that's the truth!

[@jebes909090]

then its false. problem solved.

[@djo-dji6018]

Your comment has no meaningful content, so it's neither true nor false.

[@charlesmurphy1510]

I don’t accept paradoxes.

[@TheoLogicAlt]

Have a love-hate relationship with them.

[@sunshineo23]

At 5:00 , the word “not” is introduced and seems to have the effect of flip the meaning of what follows it. It should not be allowed because a 3rd option has already been introduced

[@CharlesHarpolek4vud]

I can easily declare but I can say anything I want and a declair either true or false or indistinguishable in many of these ways. Because I am the master of my utterances, I can declare the liars paradox as inconsequential. I also like to declare Jeffrey Kaplan has also inconsequential, rudely over educated, and incapable of functioning among men like me. Of course I declare men like me to be superior to Jeffrey Kaplan, I can choose not to deal with a crazy man who is both an encounter criminal and rudely over educated. I can create a set of Jeffrey Kaplan that I can safely dismiss as being a dangerously speaking human being. Because Jeffrey Kaplan does not join me in choosing to make whatever statement I wish, I can safely dismiss this dangerous and rudely over educated person. whew; Brushing my hands together, I relax into a satisfied smile.

[@haroldostenger5160]

There is an additional reference problem when substituting. This sentence is strange (a). Then, substituting, it yields "this sentence is strange is strange (b)". Now, I want to do the new substitution. Does "this sentence" refer to (a) or (b) ?

[@magicofreality]

What about Gödel’s incompletness theorem? Does it concern this problem?

[@Velvet_Torpedo]

Philosophy or semantics? Of course we need words and language to express ideas but I often wonder how much of philosophy is really our own making and limited by the terminology and vocabulary we use Could there be something like Plato's Forms and a perfect sentence? It's fascinating! I wonder in the grand scheme of the universe if there actually are answers to paradoxes, or if we have just made paradoxes up because of our limits on vocabulary and terminology.

[@DJ.Michelle]

This is my fave video of yours, to date!

[@Sharpspider543]

Isn't the pair of sentences still self referential because if you do the same thing as with fribble with both you never end

[@MatthewCampbell765]

I have a few solutions to this, I might post a few of them in different comments, but: One possibility is that there's a finite speed to the cause-and-effect of sentences here. Let's say we go with the dual-sentence variation: The sentence below is false The sentence above is true There might be a finite speed at which the two sentences affect each other. Think of it less as a conventional statement and more as a set of infinitely repeating instructions, like: If switch A is set to 'on', set switch B to 'off' (and do the reverse if not). If switch B is set to 'off', set switch 'A' to 'off' (and do the reverse if not). You follow these sets of instructions as long as you like. So, the sentence pair above rapidly switches between being true and false as rapidly as the reader is willing to imagine them.

[@horrid8024]

I am having a problem with the 2-sentence example, which I am going to pick up, since it is presented here. Maybe there might be a pair of expressions/sentences that work and probably someone can clarify where I am wrong or expand on it to clarify why the example still works. So, I can accept the premise that 2 sentences might remove the self-reference problem, but in the given example and explanation I still see self-reference and I cannot see how to remove it. First, the word "below" is too unspecific. It could mean any sentence below the sentence that says it. There could be 15 other sentences. So it would need to be more specific. So what could you do? You could say "the sentence immediately below this sentence" => self-reference, doesn't work. Maybe give them numbers/names/symbols and say "sentence number 2 of this sequence". But that would be self-reference, as well, because the whole sequence would contain sentence number 1 as well. Basically what I want to say is that this example of two sentences only works, because it is a self-defined, self-contained closed system of two sentences in which you can go around the problem, that you have to relatively refer to the second sentence within the first sentence. And that, I think only works without self-reference within the fist sentence, if the system is closed like this. But a closed system, where there is only one option of relative reference to avoid self-reference can firstly not be generalized and secondly it shows characteristics of a self-reference, that is just one level above the two sentences and takes that burden for them. Just like my sequence example above, this closed system makes both sentences connected by definition, but it is not as obvious. So ultimately the upper sentence can only refer to the lower sentence without self-reference, because they are stuck together by a self-referencing system. Without self-reference you could not define that system, and thus self-reference is not eliminated. Or can you? If someone can logically explain how to make a set of expressions refer to each other without self-reference by defining itself as part of the set, that'd be nice. :)

[@dinoeebastian]

couldn't you say, no looping unless there's a delay, so the result of a sentence can never effect itself unless you delay. This would then mean that the sentences "The sentence to the right is false." and "The sentence to the left is true." would just be invalid, or it would cycle between being true and false with some delay between them, or is there something that beats that as well?

[@gewitterhund3164]

Funny: The algorythm of YT suggested me your Russel's paradox video (sets and stuff) and i wanted to comment with "This sentence is false". Then i checked your channel and chose the first video that got my attention and it was this. So i guess i can save my comment... 😏 Edit: Haha, you even mentioned the video yourself ^^

[@HeinrichHeinrichs]

4:20 From my perspective it's from. Because you first have to look at if true or false. If not true, that means it false. From this point conclusion is drawn. Just if at first the claim is not true and not false, then it can be neither true nor false (third category)

[@Mynamewasusedalready]

Picard would never have existed without Kirk. That sentence is true!

[@PRGME7]

I came up with a similar paradox. Say we make an AI that is not conscious but seems it. What if the AI said “I am not self aware”?

[@Leafsdude]

Maybe I missed something, but isn't the path from t-schemas the translation of the paradox: "The sentence below" and "the sentence above", turning the whole thing semantically void as far as the issue of truth, showing the very problem with the sentences themselves? I was expecting something on this and some explanation of why that's a failure, but the video then just...ended. Which has me confused. ... ... Yeah, I probably missed something...

[@indrapolak5042]

May I point to a relevant classical text on this subject "Classical Recursion Theory" by P. Odifreddi. Its about how you define functions in such a way that they still have some meaning. An example of a function losing its meaning is by defining it in terms of itself, as you demonstrated by the need to "unfold" a placeholder indefinitely. As mentioned by others, recursion is a way of defining functions very elegantly in mathematics and in computer science, but you have to be careful to make sure the function you are defining "in terms of itself" has only one possible meaning. For instance, the function defined by f(0) = 0 and f(x) = f(x-1) + 1 for all x>0. This is a well defined recursive function (say f(2) = f(1)+1 = f(0)+1+1 = 0 + 1 + 1 = 2.) The text describes various ways to define various classes of functions which are capable of computing various things, and naturally we come across halting problems and godels famous incompleteness theorem that also is the main star of Godel, Escher Bach. Then you learn that sets and more importantly the recursive enumerable ones are in fact the same thing so we reach full circle with your video's on the liar paradox and rephrasing set theory as predicates. Its all in the book :P In computer science we are mostly interested in recursive functions that do terminate and not result in an infinite loop, although sometimes infinite loops are used but can be exited by user intervention and that is fine, but in such loops recursion is never used since that would lead to so called "stack overflow", unless optimized away by a good compiler.

[@Snidbert]

If you’re willing to accept “neither true nor false” as an option, it shouldn’t be that much of a stretch to accept “neither true nor not true.” Also, the two-sentence formulation of the liar paradox is still self-referential, just with extra steps. “The sentence below” is just shorthand for the sentence “The sentence above is true,” wherein the phrase “the sentence above” is shorthand for “the sentence below is false.”

[@DogaCol]

Isn’t it self-reference with extra steps when we use two sentences referring to each other?